Flexibility as an indicator of feasibility of zeolite frameworks

The online database at www.hypotheticalzeolites.net contains over two million unique hypothetical zeolite structures. By a simple flexibility calculation, we have been able to identify a subset of 5824 flexible structures that exhibit characteristics for synthetic feasibility as zeolites. 78 out of 97 officially approved zeolite framework types that occur in the database are included in this flexible subset, including many that have been synthesized only in mixed and nonsilicate compositions. This suggests that framework flexibility (a geometric property) provides an effective filtering criterion for identifying realizable zeolite frameworks, independent of an accurately computed framework energy. We present statistics on internal surface area, occupiable volume, diameters of maximum included spheres, and maximum free spheres for the flexible subset and compare with the values for the approved framework types.